The present invention relates to tank pressure control systems and particularly to an apparatus for controlling flow of fuel vapor and liquid fuel through an aperture in a fuel tank. More particularly, the present invention relates to a tank venting control assembly that closes automatically to prevent discharge of fuel vapor and liquid fuel from the fuel tank during refueling, agitation of the tank, or vehicle rollover, while opening automatically to allow discharge of fuel vapor with minimum discharge of liquid fuel during normal operation of the vehicle.
Controlling fuel vapor pressure in vehicle fuel tanks has long been an objective for automobile manufacturers and suppliers of fuel systems components. Fuel vapor can be created in the fuel tank by temperature differences between the fuel tank and liquid fuel from a fuel pump, as well as by sloshing and agitation of the fuel tank during normal vehicle operation. The pressure build-up resulting from the creation of new fuel vapors must be properly relieved. For this reason, some vehicle fuel systems are equipped with pressure relief valves capable of discharging a relatively large amount of fuel vapor through an outlet which is typically of relatively small diameter due to limitations on space available in the vicinity of the fuel tank.
Once the fuel vapor has been discharged from the fuel tank, the vapor must be adequately captured and stored to assure compliance with air pollution regulations. In some vehicle fuel systems, discharged fuel vapor is exhausted to a charcoal-filled vapor recovery canister designed to capture and store fuel vapor. These so-called "on-board" fuel vapor recovery systems are disclosed, e.g., in U.S. Pat. Nos. 4,770,677; 4,816,045; and 4,836,835.
The attempt to achieve high fuel vapor flow rates has spawned a number of collateral problems in the design of venting control assemblies for fuel systems. One major problem with high flow capacity closure assemblies is that they tend to allow liquid fuel carryover. That is, droplets of liquid fuel become entrained in fuel vapor upon sloshing or agitation of the fuel tank and are discharged through the discharge orifice.
Liquid fuel carryover is undesirable for a number of reasons. For instance, the liquid droplets can be deposited in the vapor recovery canister, where they are likely to impair the canister's effectiveness in capturing fuel vapor.
In addition, it has long been appreciated that venting control assemblies should provide means for preventing liquid fuel leakage during tilting or rollover of the vehicle (see, e.g., U.S. Pat. Nos. 4,351,350; 4,655,238; 4,760,858). However, venting control assemblies allowing discharge of high mass flow rates of fuel vapor should also provide means for reducing discharge of liquid fuel even when the fuel tank is in its normal, upright position.
One object of the present invention is to provide a tank venting control assembly having a relatively small orifice diameter but nevertheless being configured to discharge a relatively large volume of fuel vapor from a fuel tank during development of fuel vapor pressure in the tank in excess of a predetermined amount.
Another object of the present invention is to provide a venting control assembly that automatically closes during sloshing or agitation of liquid fuel in the fuel tank to minimize carryover of liquid fuel from the fuel tank through the discharge orifice to a vapor recovery canister.
Still another object of the present invention is to provide a venting control assembly that automatically closes during vehicle tilting or rollover.
Yet another object of the present invention is to provide a closure assembly that automatically closes at a predetermined liquid fuel level during tank refueling operations to prevent a fuel pump operator from overfilling the tank.
According to the present invention, an apparatus is provided for controlling flow of fuel vapor and liquid fuel through an aperture in a fuel tank. The apparatus includes a housing and a float valve movable in the housing. The housing is mounted in the aperture and is formed to include an outlet. The float valve is movable in the housing between a closed position blocking flow of fuel vapor and liquid fuel through the outlet and an open position allowing flow of fuel vapor through the outlet. The float valve is formed to include a float chamber.
The apparatus further includes a ball positioned in the float chamber and means for supporting the ball in the float chamber so that the ball is able to move in the float chamber in response to movement of the fuel tank. The ball moves so as to urge the float valve to its closed position. The supporting means is movable relative to the housing.
In operation of the apparatus of the present invention during conditions of sloshing or agitation, the supporting means will move upwardly relative to the housing in the float chamber, thus moving the ball and the float valve upwardly so that the float valve blocks discharge of fuel vapor and liquid fuel through the outlet. Advantageously, such blockage of the outlet is effective to minimize liquid fuel carryover from the fuel tank to a fuel vapor recovery canister connected to the fuel tank through the vent assembly.
Further, the float valve moves quickly under its own weight to reopen the outlet when sloshing or agitation ends or the fuel level in the fuel tank decreases and the risk of liquid fuel carryover to the vapor recovery canister is lessened. When the float valve returns to its open position, venting of fuel vapor can resume at the desired high rate.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.